Stripline Crosstalk Calculator estimates backward crosstalk voltage and dB attenuation induced on a victim trace by a neighboring aggressor signal on a multilayer PCB stripline.
Stripline Crosstalk Calculator: Estimating Backward Noise Between Coupled PCB Traces
This tool estimates near-end (backward) crosstalk on a stripline PCB — the noise voltage induced on a victim trace by an aggressor signal routed parallel to it between two reference planes. PCB and signal integrity engineers use it during stackup and routing review to check whether traces run close enough together to violate a noise budget.
How to Use
Enter source rise time, source voltage, coupled length, trace spacing, each trace’s height above its nearest plane, total substrate height, and dielectric constant. The calculator returns coupled voltage on the victim trace and total attenuation in dB between the aggressor and victim signal.
Formula
The model follows the backward-crosstalk method in Howard Johnson and Martin Graham’s High-Speed Digital Design. Round-trip delay across the coupled length is calculated first, then compared against source rise time to determine whether crosstalk is still building with length (unsaturated) or has hit its ceiling (saturated).
$$T_{RT} \approx 2 \times 1.017\sqrt{\varepsilon_r} \times L$$
where $L$ is coupled length in feet and $T_{RT}$ is in nanoseconds.
$$d_{eff} = \sqrt{S^2 + (h_2 – h_1)^2}$$
$$h_{1,eff} = \frac{h_1(H-h_1)}{h_1+(H-h_1)}, \quad h_{2,eff} = \frac{h_2(H-h_2)}{h_2+(H-h_2)}$$
If $T_{RT}/t_r \le 1$ (unsaturated):
$$CT_{dB} \approx 20\log_{10}\left(\frac{1}{1+\dfrac{d_{eff}^2}{h_{1,eff}\,h_{2,eff}}} \times \frac{T_{RT}}{t_r}\right)$$
If $T_{RT}/t_r > 1$ (saturated, past the critical length):
$$CT_{dB} \approx 20\log_{10}\left(\frac{1}{1+\left(\dfrac{d_{eff}^2}{h_{1,eff}\,h_{2,eff}}\right)^{2}}\right)$$
Coupled voltage applies the same ratio directly against source voltage instead of in dB. Critical length is the coupled length where $T_{RT}$ equals $t_r$: $L_{sat} \approx \dfrac{t_r}{2 \times 1.017\sqrt{\varepsilon_r}}$ (feet). The most common input mistake is entering edge-to-edge trace spacing when the formula’s separation term is meant to be measured on the same centerline basis as $d_{eff}$ — mixing the two skews the coupling ratio and can understate crosstalk.
One interaction that’s easy to miss: $d_{eff}$ folds vertical stagger into the separation term through $\sqrt{S^2+(h_2-h_1)^2}$. If the aggressor and victim sit on different layers at unequal heights above the reference plane, that height offset adds to the effective separation exactly like widening the lateral pitch — so staggering trace layers works as a crosstalk mitigation in its own right, separate from spreading traces further apart.
FAQ
What’s the difference between backward and forward crosstalk?
Backward (near-end) crosstalk propagates toward the aggressor’s driver and saturates past the critical length. Forward (far-end) crosstalk travels toward the receiver and, in stripline’s uniform dielectric, is theoretically near zero rather than saturating.
Why does crosstalk stop increasing after a certain trace length?
Once round-trip delay across the coupled length equals the source rise time, the induced pulse reaches its maximum width and amplitude. Adding more coupled length past that critical length doesn’t add more crosstalk voltage.
Does doubling trace spacing halve the crosstalk?
No. Spacing enters the formula as $d_{eff}^2$, so the relationship is nonlinear. The size of the reduction from any given spacing increase depends on where the current ratio sits relative to the effective trace heights.
What counts as source rise time in this calculator?
It’s the transition time of the aggressor driver’s output edge, not the receiver’s edge rate. It sets how fast the aggressor voltage changes and determines whether the coupled length is saturated.
How is stripline crosstalk different from microstrip crosstalk?
Stripline’s symmetric dielectric keeps forward crosstalk close to zero, so backward crosstalk dominates. Microstrip’s mixed air/substrate dielectric creates a velocity mismatch that also produces meaningful forward crosstalk.